HHC Aeroacoustic Rotor Tests in the German-Dutch Wind Tunnel: Improving Physical Understanding and Prediction Codes

Within an international research program jointly conducted by US Army's Aeroflightdynamics Directorate (AFDD), NASA Langley, DNW, ONERA and DLR, the effects of a higher harmonic blade pitch angle on the rotor noise and vibrations were internsively studied. The program, denoted with Higher Harmonic Control Aeroacoustic Rotor Tests (HART) comprised both theoretical and experimental activities,the latter ones being represented by a comprehensive wind tunnel test campaign. Besides aeroacoustic measurements it comprised flow visualization tests and flow field measurements which were applied along with optical methods to determine the blade deflections. The measurements were preceded by extensive simulations performed with the analytical models of the individual participating organizations. Within these simulating different models for the rotor downwash, the blade aerodynamics and the rotor dynamics were used, leading to a very comprehensive theoretical data base